CHAPTER 7
Bonding
7.3 Molecular
Geometry and
Lewis Dot Structures
Each water molecule contains one oxygen atom and two hydrogen atoms.
One central oxygen atom
One hydrogen atom on either side
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7.3 Molecular Geometry and Lewis Dot Structures
Each water molecule contains one oxygen atom and two hydrogen atoms.
One central oxygen atom
Why can’t a water
molecule be like this?
One hydrogen atom on either side
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7.3 Molecular Geometry and Lewis Dot Structures
The oxygen forms one bond
One hydrogen forms two bonds
One hydrogen forms one bond
The Lewis structures indicate
that it is not possible
Why can’t a water
molecule be like this?
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7.3 Molecular Geometry and Lewis Dot Structures
Lewis structures for individual atoms are like puzzle pieces.
Put them together to form molecules.
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7.3 Molecular Geometry and Lewis Dot Structures
Use Lewis structures to predict:
1) the chemical formula
The chemical formula for water is H2O
(2 hydrogen atoms for every 1 oxygen atom)
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7.3 Molecular Geometry and Lewis Dot Structures
Use Lewis structures to predict:
1) the chemical formula
2) the bonding pattern
Oxygen must be the central atom
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7.3 Molecular Geometry and Lewis Dot Structures
Use Lewis structures to predict:
1) the chemical formula
2) the bonding pattern
3) the shape of the molecule
H2O is flat and bent
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7.3 Molecular Geometry and Lewis Dot Structures
Use Lewis structures to predict:
1) the chemical formula
2) the bonding pattern
3) the shape of the molecule
H2O is flat and bent
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7.3 Molecular Geometry and Lewis Dot Structures
Consider the chemical formula C2H6O
Does this
look right?
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7.3 Molecular Geometry and Lewis Dot Structures
Consider the chemical formula C2H6O
Ethanol
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7.3 Molecular Geometry and Lewis Dot Structures
Consider the chemical formula C2H6O
Could this
be right
too?
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7.3 Molecular Geometry and Lewis Dot Structures
Consider the chemical formula C2H6O
Dimethyl ether
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7.3 Molecular Geometry and Lewis Dot Structures
Two isomers of C2H6O
Ethanol
Dimethyl ether
isomer: a specific structure of a molecule, only used when
a chemical formula could represent more than one
molecule.
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7.3 Molecular Geometry and Lewis Dot Structures
Give three isomers for the formula C3H8O. Show the Lewis dot diagram
and the structural formula for each molecule.
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7.3 Molecular Geometry and Lewis Dot Structures
Give three isomers for the formula C3H8O. Show the Lewis dot diagram
and the structural formula for each molecule.
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Asked:
The Lewis dot diagrams and structural formulas for the three
molecules represented by the formula C3H8O
Given:
Carbon has four unpaired electrons, hydrogen has one, and
oxygen has two. Three carbons, eight hydrogens and one
oxygen form each molecule.
Relationships:
The atoms will bond together such that all unpaired electrons
will be paired up with electrons from other atoms.
7.3 Molecular Geometry and Lewis Dot Structures
Give three isomers for the formula C3H8O. Show the Lewis dot diagram
and the structural formula for each molecule.
Asked:
The Lewis dot diagrams and structural formulas for the three
molecules represented by the formula C3H8O
Given:
Carbon has four unpaired electrons, hydrogen has one, and
oxygen has two. Three carbons, eight hydrogens and one
oxygen form each molecule.
Relationships:
The atoms will bond together such that all unpaired electrons
will be paired up with electrons from other atoms.
Solve:
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7.3 Molecular Geometry and Lewis Dot Structures
Multiple bonds
Sharing a pair of electrons is called a single bond.
Carbon, nitrogen and oxygen commonly form double and triple bonds.
Double bond
Triple bond
(2 pairs of electrons)
(3 pairs of electrons)
Ethene
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Ethyne
7.3 Molecular Geometry and Lewis Dot Structures
Acetonitrile (C2H3N)
Bond atoms
together, forming
single bonds.
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7.3 Molecular Geometry and Lewis Dot Structures
Acetonitrile (C2H3N)
Bond atoms
together, forming
single bonds.
Form double bonds
by bringing together
single electrons
from atoms that are
already bonded.
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7.3 Molecular Geometry and Lewis Dot Structures
Acetonitrile (C2H3N)
Bond atoms
together, forming
single bonds.
Form double bonds
by bringing together
single electrons
from atoms that are
already bonded.
Form triple bonds
with any remaining
single electrons.
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7.3 Molecular Geometry and Lewis Dot Structures
Acetonitrile (C2H3N)
Bond atoms
together, forming
single bonds.
Form double bonds
by bringing together
single electrons
from atoms that are
already bonded.
Form triple bonds
with any remaining
single electrons.
Write final Lewis dot
structure and
structural formula.
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7.3 Molecular Geometry and Lewis Dot Structures
Formaldehyde (CH2O)
Bond atoms
together, forming
single bonds.
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7.3 Molecular Geometry and Lewis Dot Structures
Formaldehyde (CH2O)
Bond atoms
together, forming
single bonds.
Form double bonds
by bringing together
single electrons
from atoms that are
already bonded.
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7.3 Molecular Geometry and Lewis Dot Structures
Formaldehyde (CH2O)
Bond atoms
together, forming
single bonds.
Form double bonds
by bringing together
single electrons
from atoms that are
already bonded.
Form triple bonds
with any remaining
single electrons.
Write final Lewis dot
structure and
structural formula.
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7.3 Molecular Geometry and Lewis Dot Structures
Use Lewis structures to predict:
1) the chemical formula
2) the bonding pattern
3) the shape of the molecule
H2O is flat and bent
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7.3 Molecular Geometry and Lewis Dot Structures
Valence
Shell
Electron
Pair
Repulsion
H2O is flat and bent
The lone pairs of electrons are not involved
in bonding, but affect the shape of the molecule.
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7.3 Molecular Geometry and Lewis Dot Structures
Valence
Shell
Electron
Pair
Repulsion
H2O is flat and bent
VSEPR: a theory that states that the shapes of molecules
are dictated, in part, by the repulsion of the shared
electrons and the unshared pairs of electrons.
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7.3 Molecular Geometry and Lewis Dot Structures
Similar charges repel each other.
Identify regions of electron density to predict the
molecular geometry.
2 REGIONS
Carbon dioxide
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7.3 Molecular Geometry and Lewis Dot Structures
Similar charges repel each other.
Identify regions of electron density to predict the
molecular geometry.
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2 REGIONS
3 REGIONS
Carbon dioxide
Formaldehyde
7.3 Molecular Geometry and Lewis Dot Structures
Similar charges repel each other.
Identify regions of electron density to predict the
molecular geometry.
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2 REGIONS
3 REGIONS
4 REGIONS
Carbon dioxide
Formaldehyde
Methane
7.3 Molecular Geometry and Lewis Dot Structures
Two regions
Two areas of electron density repel to form linear shapes
Two charged balloons
repel in opposite
directions
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7.3 Molecular Geometry and Lewis Dot Structures
Two regions
Two areas of electron density repel to form linear shapes
Two charged balloons
repel in opposite
directions
These two regions of
electron density
repel each other,
forming a 180o angle
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7.3 Molecular Geometry and Lewis Dot Structures
Two regions
Two areas of electron density repel to form linear shapes
Two charged balloons
repel in opposite
directions
These two regions of
electron density
repel each other,
forming a 180o angle
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7.3 Molecular Geometry and Lewis Dot Structures
Two regions
Two areas of electron density repel to form linear shapes
The two 180o angles formed around each carbon
make the entire molecule straight.
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7.3 Molecular Geometry and Lewis Dot Structures
Two regions
There are two isomers for the formula C3H4. Show the Lewis dot diagram
for each molecule, and indicate which atoms are at the center of a linear
part of the molecules.
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7.3 Molecular Geometry and Lewis Dot Structures
Two regions
There are two isomers for the formula C3H4. Show the Lewis dot diagram
for each molecule, and indicate which atoms are at the center of a linear
part of the molecules.
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Asked:
The linear parts of each isomer of C3H4
Given:
There are two different isomers. Part of each molecule will be
linear. The molecules are made from three carbons and four
hydrogens.
Relationships:
Each atom that has two regions of electron density around it
will form a linear part of the molecule.
7.3 Molecular Geometry and Lewis Dot Structures
Two regions
There are two isomers for the formula C3H4. Show the Lewis dot diagram
for each molecule, and indicate which atoms are at the center of a linear
part of the molecules.
Asked:
The linear parts of each isomer of C3H4
Given:
There are two different isomers. Part of each molecule will be
linear. The molecules are made from three carbons and four
hydrogens.
Relationships:
Each atom that has two regions of electron density around it
will form a linear part of the molecule.
Solve:
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7.3 Molecular Geometry and Lewis Dot Structures
Three regions
Three areas of electron density repel to form
trigonal planar shapes
Three charged balloons
repel into the corners
of a triangle
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7.3 Molecular Geometry and Lewis Dot Structures
Three regions
Three areas of electron density repel to form
trigonal planar shapes
These three
regions of
electron density
repel, forming
120o angles
between the three
atoms bonded to
each carbon atom
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Three charged balloons
repel into the corners
of a triangle
7.3 Molecular Geometry and Lewis Dot Structures
Three regions
Three areas of electron density repel to form
trigonal planar shapes
These three
regions of
electron density
repel, forming
120o angles
between the three
atoms bonded to
each carbon atom
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Three charged balloons
repel into the corners
of a triangle
7.3 Molecular Geometry and Lewis Dot Structures
Three regions
Three areas of electron density repel to form
trigonal planar shapes
These three
regions of
electron density
repel, forming
120o angles
between the three
atoms bonded to
each carbon atom
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7.3 Molecular Geometry and Lewis Dot Structures
Three regions
Acetic acid when mixed with water is commonly known as vinegar and
has the formula C2H4O2. The correct isomer has both oxygens bonded to
the same carbon. Draw the Lewis dot structure for this isomer and
indicate where the molecule will be trigonal planar.
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7.3 Molecular Geometry and Lewis Dot Structures
Three regions
Acetic acid when mixed with water is commonly known as vinegar and
has the formula C2H4O2. The correct isomer has both oxygens bonded to
the same carbon. Draw the Lewis dot structure for this isomer and
indicate where the molecule will be trigonal planar.
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Asked:
The trigonal planar parts of acetic acid
Given:
The formula for acetic acid is C3H4O2 and both oxygens are
bonded to the same carbon.
Relationships:
Each atom that has three regions of electron density around it
will form a trigonal planar part of the molecule.
7.3 Molecular Geometry and Lewis Dot Structures
Three regions
Acetic acid when mixed with water is commonly known as vinegar and
has the formula C2H4O2. The correct isomer has both oxygens bonded to
the same carbon. Draw the Lewis dot structure for this isomer and
indicate where the molecule will be trigonal planar.
Asked:
The trigonal planar parts of acetic acid
Given:
The formula for acetic acid is C3H4O2 and both oxygens are
bonded to the same carbon.
Relationships:
Each atom that has three regions of electron density around it
will form a trigonal planar part of the molecule.
Solve:
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7.3 Molecular Geometry and Lewis Dot Structures
Four regions
The four regions of
electron density around
the carbon repel, forming
angles of 109.5o.
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Four charged balloon repel
into the corners of a
tetrahedron, rather than
lying flat in a plane
7.3 Molecular Geometry and Lewis Dot Structures
Four regions
The four regions of
electron density around
the carbon repel, forming
angles of 109.5o.
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7.3 Molecular Geometry and Lewis Dot Structures
Four regions
Lone pairs of electrons repel just like shared pairs
Lone pair of electrons
Ammonia (NH3) forms
a trigonal pyramidal
shape
The lone pair of electrons repels the shared
electrons in the H–N bonds, pushing
the hydrogens away from the lone pair
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7.3 Molecular Geometry and Lewis Dot Structures
Four regions
Different geometries formed by atoms with four regions of electron density
Tetrahedral
Trigonal pyramidal
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Bent
7.3 Molecular Geometry and Lewis Dot Structures
What shapes are formed within the isomer of C4H5NO, which has a triple
bond connecting nitrogen?
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7.3 Molecular Geometry and Lewis Dot Structures
Four regions
What shapes are formed within the isomer of C4H5NO, which has a triple
bond connecting nitrogen?
Solve:
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7.3 Molecular Geometry and Lewis Dot Structures
Use Lewis structures to predict:
1) the chemical formula
2) the bonding pattern
3) the shape of the molecule
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7.3 Molecular Geometry and Lewis Dot Structures